1. Field of the Invention
The present invention relates to a broadcast signal receiver corresponding to multi-directional antenna.
2. Description of the Related Art
In recent years, a broadcast signal receiver called “set top box” (it is designated by a reference of STB in figures) corresponding to multi-directional antenna is put in practical use and familiarized. The multi-directional antenna is connected to the broadcast signal receiver through an antenna controller, so that an effective signal receiving direction thereof is controlled.
FIG. 3 shows a connection among the multi-directional antenna, the antenna controller and the broadcast signal receiver. The antenna controller 3 and the broadcast signal receiver 1 are connected with a modular cable 4 and a coaxial cable 5 each other. The modular cable 4 has a control signal transmission line 13 used to transmit a control signal for controlling the multi-directional antenna 2, a source voltage line 14 used to apply a predetermined source voltage, and a grounding line 15 connected to control a gland of the broadcast signal receiver 1. Broadcast signal (RF signal) received with the multi-directional antenna 2 is transmitted to the broadcast signal receiver 1 through an inside conductor of the coaxial cable 5.
The multi-directional antenna 2 is connected to the antenna controller 3 with a coaxial cable 6. An inside conductor of the coaxial cable 6 is used for transmitting the RF signal received by the multi-directional antenna 2 to the antenna controller 3, and an outside conductor thereof is used for applying a predetermined driving voltage (for example 12V) to the multi-directional antenna 2 when an effective signal receiving direction of the multi-directional antenna 2 is switched.
The coaxial cables 5 and 6 are connected to the antenna controller 3 by coaxial connectors 8 and 9. However, by specifications of the antenna controller 3, the same kinds of connectors are used for the coaxial connectors 8 and 9. Therefore, there is a possibility that the coaxial cable 5 which should be connected to the coaxial connector 8 of the antenna controller 3 may erroneously be connected to the coaxial connector 9. If such a faulty wiring is passed undetected, the driving voltage used for switching the effective signal receiving direction of the multi-directional antenna 2 is applied to a tuner circuit of the broadcast signal receiver 1, so that the tuner circuit may be damaged. In addition, an output line of the power supply of the broadcast signal receiver 1 is short circuited to the ground, so that an over current flows to the power source circuit and so on of the broadcast signal receiver 1, and the broadcast signal receiver will break down.
By the way, Japanese Laid-Open Patent Publication No. 11-249763 shows a computer which supplies a power to a monitor display apparatus after confirming that the computer and the monitor display apparatus are properly connected. In addition, Japanese Laid-Open Patent Publications No. 2003-125023, No. 2001-25149, No. 2002-262448, and No. 2003-189467 respectively show a technique to intercept the over current by a polymeric protection switched.